Print hammer rapid reset means in high speed printers



NOW 1967 w. L. POLAND 3,351,007

I PRINT HAMMER RAPID RESET MEANS IN HIGH SPEED PRINTERS Filed Oct. 18, 1965 2 Sheets-$heet 1 INVENTOR William I Poland BY W QM ATTORNEY Nov. 7, 1967 w. L. POLAND 3, 5

PRINT HAMMER RAPID RESET MEANS IN HIGH SPEED PRINTERS Filed Oct. 18, 1965 2 Sheets$1heet 2 Fig. 5

I 0 t. Fig.5a

Fig.5b

0 94 a Fig.5c

INV EN TOR William L Poland BY My 21M ATTORNEY United States Patent 3,351,007 PRINT HAMMER RAPID RESET MEANS IN HIGH SPEED PRINTERS William L. Poland, Rochester, Mich., assignor to Control Data Corporation, Rockville, Md. Filed Oct. 18, 1965, Ser. No. 496,990 9 Claims. (Cl. 101-93) ABSTRACT OF THE DISCLOSURE A drum printer having resettable means for addressing selected hammers to prepare them for being projected from a rest position to impact the font drum and return to rest by the force of rebound from the drum. Each hammer has an elastic tail and is so constrained that the tail is flexed during projection of the hammer. The flexure energy is stored in the tail, and the path of hammer travel is such that the stored energy is dissipated as a force on the resettable means directed to reset the same.

The above path of the hammer is so designed that not only is the reset function accomplished, but also the rebound path is approximately parallel to the resultant of the rebound force component and the component introduced by the momentary clamping of the hammer face with the paper and rotating drum to minimize friction between the hammer and its guides.

This invention relates to high speed printers and particularly to improvements leading to greater reliability, higher speed, and to better print quality.

Although the principles of my invention are applicable to various types of printers, in the interest of simplicity my invention is described in connection with a high speed drum printer which is sometimes referred to as an onthe-fly printer. A typical commercially-available drum printer of this type is disclosed in US. Patent No. 3,156,- 180 and in US. Patent No. 3,185,075. As disclosed in the last-mentioned patent, a drum printer has a continuously rotating font drum together with a group of hammers confronting the drum. A record, usually composed of one or more sheets (often Fanfold) together with an inked ribbon or towel, is stepped through the print station defined as the space between the print hammers and raised characters (font) on the confronting surface of the rotating drum. In most printers of this type, selected hammers of the group are addressed in response to decoded incoming signals. Shortly thereafter the addressed hammers are driven toward the rotating drum to impact the record against the raised characters of the drum. These operations are accurately timed by means forming no part of my invention, but which are wellknown, for example, as disclosed in US. Patent No. 3,185,075.

In the usual case, the record is stationary at the instant of impact, however, the drum is continuously rotated. Generally, one full revolution of the drum is required to print a single line of characters on the record. Accordingly, for alphanumeric printing at least thirty-six hammer-address and hammer-driving cycles are required for each revolution of the drum (to print a single line). More typically sixty-four character sets and a corresponding number of cycles are used. It is evident that the speed of the hammers must be very high to obtain a satisfactory print rate.

In all drum printers of which I am aware, hammerrebound from the drum plays an important role. The hammers are driven to impact the drum in the manner of a projectile with the hammers being in substantially free flight as they travel toward the drum. Often hammerrebound is either the sole means or substantially the sole means for returning the hammers to their initial position. The behavior of the hammers is important to the quality of print. It is obviously desirable that the print be sharp, clean, uniform, well-aligned, and smudge-free. To accomplish this the hammers must fulfill a number of requirements in their operation. A few are that the hammers have uniform flight time characteristics, and that all hammers of the group impact the drum with uniform force and velocity. Not only must the dwell time at the instant of impact be predictable, but also the dwell time must be brief because the record is held at rest at the moment of impact, and the record is driven (by the hammers) against the rotating font drum. Herein lies a source of difficulty which becomes acute with increases in print ing rate as explained below.

As described in US. Patent No. 3,185,075, the hammers are ordinarily driven rectilinearly toward the drum to impact the record against the drum. The projected line of flight of each struck hammer passes through the axis of rotation of the drum, and at the instant of impact a force component is exerted on the hammers owing to the rotation of the drum and the momentary clamping action between the hammer faces, the record (including the ribbon),- and the drum. The direction of the force component imparted to the hammers is tangent to the drum at the impact points thereof. This force component, therefore, is normal to the path of flight of the hammer and consequently, it increases friction between the hammer and the hammer guides. This has an undesirable regenerative effect because it increases the dwell time of the hammer and thereby further adds to the tangential force. Thus, in the normal configuration of the drum printer, the above-defined tangential force is parasitic to the rebound force which is parallel to the flight path of the hammer, i.e. perpendicular to the tangential force.

An object of my invention is to overcome the above difliculties by (a) contraining the path of the hammer to a non-rectilinear motion (preferably arcuate) so that after impact the hammer returns along a path which is approximately parallel to the vector resultant of the rebound force and the tangential force; and/or (b) constraining the flight of the hammer in a manner such that the projected path of motion of the hammer is laterally spaced from the axis of rotation of the front drum to accomplish the achievement of (a).

To obtain high quality print impressions, all of the harnmers should have similar velocity and momentum characteristics. Velocity and momentum are influenced by several factors including friction and mass. It is easier to control mass uniformity and to maintain friction at a low predictable level by using a one-piece hammer without a fixed pivot such as disclosed in the above patents. Thus, in a preferred embodiment of my invention although the hammer travels in a curved path to effect printing, I have no fixed pivot.

The complexity of conventional drum printers is undesirably high. In addition to the obvious such as higher cost of manufacture and lower inherent reliability, complexity in the hammer assembly of a drum printer introduces undesirable friction. Since a drum printer has a large number of hammers (for example one hundred and twenty in the Control Data Corporation Model 166 Printer) there are variations in friction from hammer to hammer. As descn'bed before, this has a direct bearing on print quality.

Accordingly, a further object of my invention is to provide a one-piece, pivot-free hammer in contrast to multi-piece hammer assemblies such as used in the printers of both of the above patents. The term onepiece" as used herein includes a fabricated hammer made of more than a single part. The intention is to distinguish a a.) from a multi-piece hammer having relative motion between the pieces.

I am aware of the fact that one-piece hammers have been used before. However, it is not feasible to use prior single-piece hammers in a printer of the type where the hammers are mechanically addressed by moving them from a first position (termed latched herein) to an addressed position at which they are placed in the path of motion of a driver which strikes the addressed hammers and propels them in a direction to impact the drum and to be returned by rebound force acting on the hammers.

In prior printers such as disclosed in the previouslymentioned patents, each hammer has a hammer body with a pivoted tail. Resettable addressing means cooperate with the tail of the hammer and function in a manner such that the hammer tail is pivoted to a position at which it is struck to drive the hammer in its drum-impact flight. After forming the print impression, the hammer and its tail are returned 'by rebound force after impact, and some means must be provided for either resetting the addressing means or at least of assuring that the resettable addressing means have been reset. In the above patents the addressing means (and tail) are reset by a second blow of the hammer-driving cam.

My present invention greatly simplifies this. This simplification and the corollary improvement in reliability, are attributable to at least two things. One is the improved hammer construction and the other is the above-described non-rectilinear path which the hammer travels in moving from the addressed position to impact and from the impact position to the returned position. The configuration of my hammer cooperates with the arcuate path in a manner such that a portion of the energy to drive the hammer is stored in the hammer, and upon hammer impact the stored energy is exerted on the resettable addressing means as a force having a direction to physically reset the addressing means and thus, reset the hammer. The arrangement is such that the hammer returns to the latched position with the addressing means reset with no further steps (or structure) required.

My one-piece hammer is made of lightweight elastic material such as Delrin (described in Patent No. 3,185,- O75), or Delrin and steel. A material such as Delrin is desirable because it has a satisfactory modulus of elasticity and is light. The configuration of my hammer is such that it has a projecting portion referred to as a tail. It is important that at least this portion of the hammer be elastic because it must store energy by deflecting as impresses against the addressing means for the hammer during the forward portion of the flight of the hammer. The arcuate path of travel of the hammer is responsible for this. The hammer tail flexes (returns) in a manner such that the reaction to the flecture is exerted against the addressing means in a direction to reset the addressing means. In use, the addressing means are reset in this way at the instant of impact of the hammer with the drum or slightly thereafter. Accordingly, an object of my invention is to provide a print hammer such that it stores energy upon and/or after being struck, and the stored energy is expended to perform a function other than merely causing the hammer to rebound and return to its starting position.

Another object of my invention is to provide a print hammer configuration such that the elasticity of at least a portion of the hammer is used to store energy during hammer flight, and the stored energy is exerted as a resetting force applied to the hammer addressing means.

A further object of the invention is to provide means cooperative with a print hammer such as I have described, which require the hammer to execute a non-rectilinear path after being struck thereby causing the elastic tail of the hammer to store and apply the stored energy for any purpose useful to the printer operation.

Other objects and features of importance will be evident as description of the illustrated form of my invention proceeds. It is understood that the illustrated form of my invention is given by way of example only.

FIGURE 1 is a fragmentary sectional view of a typical prior drum printer.

FIGURE 1a is a schematic view showing the interaction of forces in the drum printer exemplified in FIG- URE 1.

FIGURE 2 is a fragmentary sectional view of a printer constructed in accordance with my invention.

FIGURE 2a is a diagrammatic view showing the interaction of certain forces in my printer.

FIGURE 3 is a sectional view taken on line 3-3 of FIGURE 1.

FIGURE 4 is a sectional view taken approximately on the line 44 of FIGURE 2.

FIGURES 5-5d are diagrammatic views showing primarily the flight of my hammer and also showing how the elasticity of the hammer is used to store and exert energy as a force directed to reset the hammer-addressing device.

FIGURE 6 is a side view of a modification of my hammer.

BACKGROUND For an understanding of a typical on-the-fly, high speed printer, attention is directed to Patent No. 3,185,- 075. FIGURES 1 and 1a herein illustrate a single hammer assembly and means to address, drive and reset the hammer as in the above patent and in Patent No. 3,156,- 180. The principle of operation of on-the-fly printers is exemplified (as to the hammer-operation) in FIGURE 1 which shows a main frame 10 on which a rotary font member such as print drum 12, is mounted. Timing belt 14 schematically represents the means for continuously rotating drum 12 to present successive longitudinal rows of raised characters 16 (font) to the print station 18. The print station is the space between the hardened impact faces 20 of hammers 22 (only one illustrated) and the confronting part of the drum. A record 24 such as a continuous sheet (usually Fan fold) is indexed or stepped through the print station 18 as is an inked medium such as a towel or ribbon 26. Tractors are ordinarily used to step the record, and I have diagrammatically illustrated these as a sprocket wheel 28 (FIGURE 2).

Hammer 22 is constrained to rectilinear motion by upper and lower guides 30 and 32 in which portions of the upper and lower edges of the flat, lightweight hammer are disposed. A lever or tail 34 is pivoted as at 36 to the rear end of hammer 22. The outer end of tail 34 supports one end of spring 38 while the opposite end of the spring is attached to an anchor 49 on the main frame of the printer. The bias of spring 38 is a direction tending to pivot tail 34 downward (as shown), however, the tail is held in the raised (latched) position by seating on an end of rocker 42 which is pivoted at 44 to frame 10. The opposite end of rocker 42 has an armature 46 which is magnetically held to pole piece 48 to establish and maintain the latched position (non-addressed) of the hammer assembly. Pole piece 48 is a part of a permanent magnet structure 50 which is pulsed by a signal applied to winding 52 to release (or repel) armature 46 in a manner identical to that described in Patent No. 3,156,180. When the armature 46 is released (or repelled) spring 38 exerts a force on tail 34 pulling it downward and this constitutes addressing the hammer. When the tail 34 is pulled down its surface 54 is moved into the path of travel of a lobe of the continuously rotating cam 56. Thus, a cam lobe, e.g. lobe 58, strikes surface 54 of tail 34 and drives hammer 22 toward drum 12 to impact record 24 and ribbon 26 against the confronting raised character 16 which at that exact moment is in alignment with the impact face 20 of the hammer. As the hammer travels toward drum 12 the hammer is in constrained free flight. Upon impact, the rebound force causes the hammer 22 and its tail 34 to return to the addressed or starting position. Upon return, the tail 34 and the resettable hammer addressing means including rocker 42 are reset to the position shown in FIGURE 1 by the succeeding lobe 60 and cam 56 striking the surface 62 of rocker 42 and pivoting tail 34 and rocker 42 about their respective pivots. Rocker 42 pivots a distance sufiicient to engage armature 46 with pole piece 48 which magnetically holds rocker 42 of the hammer addressing means in the latched position. The rocker holds tail 34 in the elevated (latched) position. Thus, the described hammer is restored to a condition such that it is prepared for the next cycle of operation identical to that described above.

Attention is now directed to FIGURE 1a as an aid to the explanation of certain observations. Hammer 22 is constrained by pairs of guides 38 and 32, to travel in a rectilinear path as shown by arrow 70. A projection of the path passes exactly through the axis 72 of rotation of drum 12 as described in Patent No. 3,185,075. At impact, the hammer face clamps the stationary record 24 (together with the ribbon or towel) against the confronting character on the font drum 12. Thus, there is a force component shown at 74, exerted on hammer 22 in a direction tending to cock the hammer in guides 30 and 32 as shown. The force component 74 is tangential to the impacted portion of the drum and therefore it is at right angles to the rebound force component 76. The resultant 78 of components 74 and 76 indicates the magnitude and more importantly, the direction of the force which is actually available to return the hammer to its initial position.

It is to be noted that record 24 can be composed of a single sheet or of many sheets with a corresponding number of carbon sheets. Thus, the hammer strikes a cushion which is inelastic and unpredictably resilient owing to the variations in the number of sheets forming the record. Therefore, the momentum of the hammer relied upon to provide the restoring or rebound energy will vary in accordance with the composition of the record 7'4. In turn, this will cause a change of magnitude and direction of resultant '78 (because the am plitude of the shock wave traveling through hammer 22 is changed). As it concerns my invention, the friction between the hammer and its guides 80 and 32 is somewhat varied and this, again, is regenerative in a sense that the parasitic tangential force represented by components 74 is a variable.

EMBODIMENT OF PRINTER The parts of my printer (FIGURE 2) which are identical to the corresponding parts of the prior art printer (FIGURE 1) are indicated by similar reference numerals. Accordingly, I have illustrated a main frame 10 supporting a font drum 12 which is continuously rotated in the illustrated direction. Record 24 together with a towel or ribbon 26 are moved through print station 18 in a manner identical to that described before.

A group of one-piece print hammers 80 (a few shown in FIGURE 4) are arranged with their faces 20 confronting the drum 12, and the addressed hammers are adapted to be driven to impact the drum (with the record and ribbon therebetween) to form the print impressions on the record. Cam 56 is used to strike the addressed hammers 80. The means to address the hammers and to reset them differ from the corresponding means of FIGURE 1 although the magnet structure 50 can be similar or identical to that of FIGURE 1. Spring 84 which is attached to one end to the single piece hammer 80 and anchored at the other end to frame 10 (for example, by clamp 87) exerts a downward and rearward force on hammer 80. Spring 84 is a hammer-return spring.

Hammer 80 is shown (FIGURE 2) in the addressed position. Addressing hammer 80 is accomplished by releasing (or repelling) armature 46 from pole piece 48 and allowing rocker 82 to turn clockwise by the action of spring 38 thereby lowering the rear end of hammer 86. The action of spring 84 also aids. The lowering of the hammer and the clockwise motion of rocker 82 can be electromagnetically achieved by repulsion between pole piece 48 and armature 46 and/or by the action of springs 38 and 84. Thus, by merely releasing armature 46, the hammer is addressed.

The upper and lower edges of the forward portion of the one-piece hammer are guided by guides 86 and 88. An intermediate part of the lower edge of the hammer is adapted to slide over ramp 9t and the rearward travel of the hammer is arrested by stop 91.

HAMMER PATH FIGURE 2a schematically represents the path of a hammer 80 which typifies one phase of my invention. As shown by direction line 94, hammer 80 is required to travel a curved path. Although the hammer traverse is a curved path, the surfaces of the impact face 20 and of the raised character 16 at the time of impact are parallel at their interface. The geometry of the hammer course with relation to the drum 12 is such that the hammer returns along a path approximately parallel to the resultant force represented by vector 78a instead of along a path parallel to the rebound force represented by vector 76a as is the case of the printer represented in FIGURE la. More particularly, at the instant of impact of the hammer with the drum 12, a tangential force represented by vector 74a is exerted on hammer 80. At the same time a rebound force represented by vector 76:: acts upon hammer 80. The resultant of these forces will have a magnitude and direction approximately as shown by vector 78a. The direction of the resultant force is parallel to the path of travel of hammer 80 in rebounding from the drum at least for the initial small fraction of motion as the hammer leaves the drum surface. This is the critical portion of hammer travel in returning from the drum to its initial position, and being very small it can be considered straight and parallel to resultant vector 78a. In comparing FIGURES la and 2a it will be seen that the dotted line projection of the path of travel of hammer 22 passes through the axis 72 of rotation of drum 12, while in my arrangement (FIGURE 2a) the corresponding dotted line projection is laterally spaced from the axis of rotation of the drum.

The fact that I use a one-piece hammer Which executes a curved path in reaching and rebounding from the drum accomplishes several things among which is a reduction in friction between the hammer and its guides caused by the above-described tangential force originating from the clamping of the paper between the rotating drum and the impact faces of the hammer. In some printers of prior design this force is so great that it pulls the record out of its tractors 28. Also, the friction between the guides and the hammer is so greatly increased by the tangential force that the hammers and/or their guides wear so badly as to have an unsatisfactorily short useful life.

HAMMER CONSTRUCTION As shown in FIGURES 2, 4-5d, hammer 80 is flat with a forward end portion of suflicient size to retain a hard (e.g. steel) impact face member 20 which is bonded to the Delrin body of the hammer. The upper and lower edges of the forward portion of the hammer are disposed with clearances between the guides 86 and 88 (FIGURE 4).

The lower edge 92 of the intermediate part of the hammer is slightly concave, and it is adapted to slide over the upper convex surface of ramp (described more fully later). The rear part of the hammer is formed with an elongated tail 94 having an enlargement 96 disposed in the yoke of rocker 82. Below the tail there is a shoulder having an impact surface 98 for the lobes of cam 56. Above surface 92 is a projection 99 which engages stop 91 to arrest the rearward motion of the hammer. The lower end of spring 84 is embedded within and bonded to the body of the hammer 80 slightly ahead of and above concave surface 92.

As will be described later, it is important that at least the tail portion of the hammer be elastic since it is used to temporarily store energy which is exerted as a force to reset the hammer-addressing structure of my printer. In the illustrated embodiments, FIGURE 2 shows the entire hammer made of the same elastic material, while FIGURE 6 shows hammer 80a in which the tail 94a is made of a spring steel strip embedded at one end into a plastic material (eg Delrin) body. Hammers 80 and 80a are functionally the same and have their corresponding features designed by corresponding numerals. For various reasons, I can use another hammer configuration (not shown) where a spring steel strip is embedded within a tail such as tail 94 of hammer 80. HAMMER PATH AND ADDRESS RESET Attention is invited to FIGURES 5d showing the behavior and functions of the hammer as it moves from the latched or rest position through impact and separation from the drum to return directly to the latched position. FIGURE 5 shows hammer 80 in its latched position. The tail 94 is retained in the yoke of rocker 82, and the position of the rocker is such that surface 92 of the hammer is held above ramp 90. In this hammer position impact surface 98 is spaced from the path of the lobes of the rotating cam 56. Springs 38 and 84 exert a downward and rearward force on the hammer 80. However, the hammer cannot move downward (to be addressed) because the lower surface of the tail enlargement 96 contacts the lower part of the yoke as indicated by the x. The hammer cannot move rearward because projection 99 engages stop 91. I have followed the convention in FIGURES 55d that pressure surfaces of significance are indicated by xs.

FIGURE 5a shows hammer 80 as it is being addressed, i.e. tilted downwardly to bring impact surface 98 into the path of travel of one of the lobes of cam 56. This is accomplished as follows: Upon an address command, armature 46 of the rocker is released from pole piece 48, and the downward component of force of spring 84 (and the force of spring 38) exerted on the hammer, rocks the yoke portion of rocker 82 downwardly with the downward motion being arrested by concave surface 92 contacting ramp 90. Accordingly, the concave and convex surfaces of the hammer and ramp form pressure surfaces as indicated by the x in FIGURE 5a. Also, the upper edge of the forward portion of the hammer contacts the top of upper guide 86. When in this position a lobe of cam 56 strikes impact surface 98 and the trajectory of the hammer is begun.

As shown in FIGURE 5b, hammer 80 is driven forward against the slight yielding opposition of spring 84. As the hammer moves forward toward drum 12 the hammer surface 92 moves up the ramp 90 thereby causing the hammer to execute a curved path. As the hammer moves toward drum 12, the tail 94 (or 9% in the case of hammer 80a) is deflected because the enlarged end 96 remains captive within the yoke of rocker 82 and the rocker offers resistance to its pivotal return to the reset position. This opposition originates from inertia, friction, and primarily the action of spring 38. The flexing of the elastic tail (internal resistance of the material) causes energy to be stored in the hammer which is expended (described later) as a force directed to reset the hammer addressing device (return rocker 82 to the position shown in FIGURE 5 FIGURE 50 shows the position of the hammer and its points of contact with ramp 90 and the upper guide 86 just as contact is being made with the drum. The action of spring 38 assures that hammer surface 92 is on the ramp at the instant of printing. As the drum is contacted, hammer 80 rebounds therefrom due to the elasticity of the drum and hammer combination, and the hammer starts to return with a momentum equal to that of impact (neglecting losses). As described before, there is a tangential force at the interface of the drum and hammer, a rebound force and a resultant of the two forces, and my hammer returns approximately parallel to the resultant. Since it is not practical, for the reasons mentioned before, to expect that the hammer return travel will be precisely parallel to the resultant force, there will be some reaction resulting in friction between the lower edge of the hammer and the lower guide 88. However, the reaction is small, the guides 86 and 88 are relatively short, and therefore there is no significant cocking of the hammer between the upper and lower guides as in FIGURE la.

At the instant of impact or very shortly thereafter as the hammer face begins to leave the drum, the reaction force storing the energy in the tail of the hammer is overcome so that the energy stored in the hammer is expended by pushing the yoke of rocker 82 in a direction such that its armature 46 contacts pole piece 48. Thus, the means which addressed the hammer originally are reset in sufficient time so that as the hammer returns from the position shown in FIGURE 5d toward the position of FIGURE 5, the yoke of the hammer guides the tail of the hammer upwardly. The result is that the hammer returns automatically to the latched position (FIG- URE 5) as its rearward motion is arrested by engaging stop 91 and by being held thereby the action of spring 84.

It is understood that the illustrated embodiment of my invention is given by way of example only. It is particularly understood that the principles of my invention apply to printers other than those which are technically considered drum printers, and that I have selected a drum printer as a convenience in explaining the background and setting of my invention. Therefore, all modifications and other variations falling within the scope of the following claims may be resorted to without departure from the protection thereof.

I claim:

1. In a printer of the type which uses a movable hammer for forming print impressions, and movable resettable means to address the hammer by displacing the hammer from a rest position to an addressed position, and means to drive the addressed hammer to perform the print impression function, the improvement comprising means for constraining the movement of said hammer to a nonrectilinear path, at least a part of said hammer being elastic and engaging said resettable addressing means, said path being so constrained relative to said resettable means that the elastic part of said hammer bears against said resettable means and deflects during a portion of the hammer movement, and the deflection of said elastic part of the hammer having a reaction against said resettable addressing means directed to reset said addressing means.

2. The printer of claim 1 wherein said constraining means include a first and a second guide together with a ramp, said guides confronting and spaced from each other and successively forming bearing surfaces for engagement by opposite edge portions of said hammer as said hammer moves in said path, and said ramp being contacted by a part of said hammer spaced from the edge portions which engage said guides to both form a bearing surface for said hammer and also to give direction to the hammer motion.

3. In a printer, an elastic hammer movable from a rest position to an addressed position thence to a print position and then directly back to said rest position, means for supporting and guiding said hammer, resettable address means for tilting said hammer in said supporting means thereby addressing said hammer, means for propelling said hammer while addressed to cause said hammer to move in a path governed by said supporting and guiding means, means responsive to the propelling means and to the guided movement of said hammer for storing elastic energy in at least a portion of said hammer as said hammer is moved from said addressed position, and said storing means enabling the stored energy to be expended as a force directed on said addressing means in a direction to reset the same by the time that said hammer returns to said rest position.

4. The printer of claim 3 wherein said supporting and guiding means include a ramp by which an edge of said hammer is guided.

5. The printer of claim 4 wherein said supporting and guiding means also include a pair of spaced guides at the forward end of said hammer.

6. The subject matter of claim 3 wherein said storing means includes an elastic tail portion of said hammer, and said resettable addressing means include a rocker which maintains engagement with said tail when said hammer moves between all of said positions.

7. The subject matter of claim 3 wherein the printer has a movable member adapted to be impacted in forming the print impressions and said path of the hammer being such that as said hammer rebounds from said movable member the .path is approximately parallel to the resultant of the force of rebound and the force exerted on the hammer by the record being clamped between the hammer and the movable member at the instant of impact.

'8. The printer of claim 3 wherein said hammer has a non-ferrous body, and said portion for storing energy is at least partially made of spring metal.

9. In a printer having a rotary member adapted to be impacted by a movable print medium during printing, a print hammer, hammer driving means to drive the hammer toward the medium, and resettable means for addressing said hammer by so positioning the hammer that said driving means can drive the hammer, the improvement comprising means for constraining the movement of said hammer to a path such that said hammer returns after impacting the medium against said rotary member along a line approximately parallel to the resultant of the forces originating from the force of the medium pull exerted on the hammer at the instant of impact and the force of hammer rebound from said rotary member, said constraining means requiring said hammer to execute a curved path of motion in moving toward and from said rotary member, said addressing means including a movable element contacting a part of said hammer and movable to displace said hammer in said constraining means to a position at which said hammer driving means can drive said hammer, at least a portion of said hammer being elastic and flexing to store energy owing to its contact with said movable element and the curved path of motion of said hammer, and said movable element of said addressing means being moved toward the reset position in response to the expenditure of the stored energy as said elastic hammer portion relaxes to its original condition after being flexed.

References Cited UNITED STATES PATENTS 2,199,561 5/1940 Fuller et al 101-93 2,328,638 9/1943 Fuller et al 101-93 2,766,686 10/1956 Fomenko et a1. 101-93 2,771,025 11/1956 Kistner et al. 10193 2,858,536 10/1958 Johnston 101-93 2,897,752 8/1959 Malmros et al 101--93 2,949,846 4/ 1960 HoiTman et a1 10193 3,128,694 4/1964 Kittler 101-93 3,145,650 8/1964 Wright 10193 3,185,075 5/1965 McGregor et al. 101-93 3,292,531 12/1966 Mutz 10193 WILLIAM B. PENN, Primary Examiner. 

1. IN A PRINTER OF THE TYPE WHICH USES A MOVABLE HAMMER FOR FORMING PRINT IMPRESSIONS, AND MOVABLE RESETTABLE MEANS TO ADDRESS THE HAMMER BY DISPLACING THE HAMMER FROM A REST POSITION TO AN ADDRESSED POSITION, AND MEANS TO DRIVE THE ADDRESSED HAMMER TO PERFORM THE PRINT IMPRESSION FUNCTION, THE IMPROVEMENT COMPRISING MEANS FOR CONSTRAINING THE MOVEMENT OF SAID HAMMER TO A NONRECTILINEAR PATH, AT LEAST A PART OF SAID HAMMER BEING ELASTIC AND ENGAGING SAID RESETTABLE ADDRESSING MEANS, SAID PATH BEING SO CONSTRAINED RELATIVE TO SAID RESETTABLE MEANS THAT THE ELASTIC PART OF SAID HAMMER BEARS AGAINST SAID RESETTABLE MEANS AND DEFLECTS DURING A PORTION OF THE HAMMBER MOVEMENT, AND THE DEFLECTION OF SAID ELASTIC PART OF THE HAMMER HAVING A REACTION AGAINST SAID RESETTABLE ADDRESSING MEANS DIRECTED TO RESET SAID ADDRESSING MEANS. 